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325xi-SteelGray
01-08-2003, 05:51 PM
Can anyone explain why the brake pad sensors aren't "triggered" before they ruin the rotors? I just had my rear pads and rotors replaced (44k) but the sensor light never came on on the dash board. For future reference, should I be inspecting the pads so I don't ruin rotors? If so, how?

Thanks!

Rufus330Ci
01-08-2003, 06:07 PM
The easiest way to check brake pad wear is to take off the wheel (with a good jack supporting the car of course) and use a flashlight, lay on the ground and check the thickness of the brake pad. In the 'ole days' a couple years ago and probably on most cars today there is a safety indicator just a metal extension that will rub on your rotor which causes the whine sound that lets you know its time. I'd say if you notice the pad wear is less then the thickness of 2-3 pennies together its time to change up.

Bruce
01-08-2003, 06:09 PM
Originally posted by 325xi-SteelGray
Can anyone explain why the brake pad sensors aren't "triggered" before they ruin the rotors? I just had my rear pads and rotors replaced (44k) but the sensor light never came on on the dash board. For future reference, should I be inspecting the pads so I don't ruin rotors? If so, how?

Thanks!

BMW pads and rotors are designed to be replaced at the same time. BMW does not recommend turning rotors and reusing them. When the brake sensor light comes on it is time for new pads AND rotors. Hoenestly the parts are THAT expensive and the project is pretty cheap if you DIY.

rwg
01-08-2003, 06:12 PM
Umm - two things.

BMW brake pads don't have noise making wear indicators (at least the don't on the e46). They have electronic brake wear sensors instead - that apparently don't always work.

Never, ever get under a car that is "on a good jack." Use a jack stand. They are very inexpensive and you don't risk your life.

Inspecting the brakes is easy if you take a wheel off and have a flashlight handy, but you have to have something to compare the thickness of your pads to. If you have never seen a new pad, you won't know whether what you are seeing is a lot or a little. The pads have a bevel on each edge when new - when that angled portion is gone, you might want to start thinking about having a mechanic take a look. If you do inspect the brakes yourself, don't forget to inspect the inside pad as well as the outside pad. The inside pads sometimes wear faster and are not as easy to see.

Kaz
01-08-2003, 06:41 PM
If the rotor thickness is within spec and not out of round or out of true I don't really see any point in replacing them when the pads go just because.

Pinecone
01-08-2003, 06:46 PM
The BMW electronic sensor only works on one front and one rear. So the other side could be gone, but the sensor not light up.

Rufus330Ci
01-08-2003, 08:33 PM
Originally posted by rwg
Umm - two things.

BMW brake pads don't have noise making wear indicators (at least the don't on the e46). They have electronic brake wear sensors instead - that apparently don't always work.

Never, ever get under a car that is "on a good jack." Use a jack stand. They are very inexpensive and you don't risk your life.

Inspecting the brakes is easy if you take a wheel off and have a flashlight handy, but you have to have something to compare the thickness of your pads to. If you have never seen a new pad, you won't know whether what you are seeing is a lot or a little. The pads have a bevel on each edge when new - when that angled portion is gone, you might want to start thinking about having a mechanic take a look. If you do inspect the brakes yourself, don't forget to inspect the inside pad as well as the outside pad. The inside pads sometimes wear faster and are not as easy to see.

Well I learn something everyday :O) I didn't know you had to change both rotors and pads......... I was basing my answer on my other cars that are alot older, they didn't have "sensors" back then you knew it was time when the tab was wearing against the rotor. I can normally tell by just looking at a pads on my other cars if it needs changed.. The Bimmers so new I haven't had the wheel off to see this situation we are discussing, excuse me.... But can someone else verify do you really have to change pads and rotors?!?!?!?!?? Thats about gay......

Chris330Ci
01-09-2003, 05:31 AM
Originally posted by Pinecone
The BMW electronic sensor only works on one front and one rear. So the other side could be gone, but the sensor not light up.

Quick question...I know I've heard rumors that track days that are excessively hard on brakes can 'cook' these sensors. Anyone have any info to back this up? Sounds like a long shot, but possible... :dunno:

Desertnate
01-09-2003, 07:42 AM
Originally posted by Rufus330Ci
The Bimmers so new I haven't had the wheel off to see this situation we are discussing, excuse me.... But can someone else verify do you really have to change pads and rotors?!?!?!?!?? Thats about gay......

Yes, you do have to replace both at the same time! The service person at the dealership I go to told me that the fronts you replace every time you replace the pads and the rears every other because apperently they are a little thicker and don't wear as fast. I had to replace my fronts at around 40~45K miles, which tends to be far longer than most people last (I was out of the country for a year and my wife drove the car :eeps: )

The reason you have to replace both the rotors and the pads is that they both wear down. They are rather like a matched set and wear out together. Up side is that you get GREAT breaking, down side is replacing both. You may get away without having the rotors replaced, but be very careful and ensure the thickness is within spec.

325xi-SteelGray
01-09-2003, 08:52 AM
BMW brake pads don't have noise making wear indicators (at least the don't on the e46).

I was referring to the sensors that light up on the dash board. (I have seen the light on the dash previously, when the dealer broke the sensor during Inspection I.) Unfortunately, the only sound warning I received was the metal on metal grinding!

Thanks for the input all!

The HACK
01-09-2003, 08:55 AM
Originally posted by Chris330Ci
Quick question...I know I've heard rumors that track days that are excessively hard on brakes can 'cook' these sensors. Anyone have any info to back this up? Sounds like a long shot, but possible... :dunno:

False.

These "sensors" are just simple copper wires with insulation. Basically there's a small electrical current that's sent to the wire, but since it's insulated, the circuit is never completed.

Once the insulation is cut through by the brake wearing down, and the wire is exposed and contacts the rotor when braking, the wire contact with the rotor completes the circuit (providing a source for GROUND signal) and that triggers the brake warning every time the brake is applied. Once the brake warning "wire" got worn down so much that the rotor has cut through the wire, the lack of signal when brake is applied will cause the brake warning light to be on at all times.

Unless your brake can heat up high enough to melt the insulation away or melt copper, there's no way that excessive brake use on the track can possibly damage the sensors.

SG1
01-09-2003, 12:34 PM
"Once the brake warning "wire" got worn down so much that the rotor has cut through the wire, the lack of signal when brake is applied will cause the brake warning light to be on at all times. "

Do you mean the brake warning light will of "OFF" at all times once the rotor has cut thru the wire? I'm not sure I follow...

The HACK
01-09-2003, 12:46 PM
Originally posted by SG1
"Once the brake warning "wire" got worn down so much that the rotor has cut through the wire, the lack of signal when brake is applied will cause the brake warning light to be on at all times. "

Do you mean the brake warning light will of "OFF" at all times once the rotor has cut thru the wire? I'm not sure I follow...

This is the way I think it works...

Once the insulation has been worn off, and as the brakes are applied the light will come on, and go off when the lights are not applied. The on board ECU logs that the brake sensor has gone off.

Basically, when the rotor has worn completely through the wire, when brakes are applied there will no longer be a signal being sent to the ECU thus the ECU can interpret THAT code after the brake sensors has gone off and assumes the wire is cut, and the warning light will stay on CONSTANTLY.

Thus, if the sensor was worn down and needed replacement, it's not just a simple plug and play...the ECU must be cleared of that fault code otherwise it'll think the sensor has been worn completely through (because it doesn't send signals anymore when brakes are applied).

At least that's the way I understand it to work.

SG1
01-09-2003, 01:05 PM
Hack,

What if you replaced the pads yourself at the first sight of the brake warning light or even at a later date (before the wire is cut)? Would the computer also assume that the wire is broken and thus keep the warning light lit?

The HACK
01-09-2003, 01:18 PM
Originally posted by SG1
Hack,

What if you replaced the pads yourself at the first sight of the brake warning light or even at a later date (before the wire is cut)? Would the computer also assume that the wire is broken and thus keep the warning light lit?

If the brake warning light came on, and you replace the pad AND the brake sensor, then the computer is going to assume the sensor is still cut all the way through and continue to keep the warning light lit at all times.

Hence you will need to take a trip down to the dealership service department and have them RESET your ECU's fault code for you.

elbert
01-09-2003, 06:53 PM
Originally posted by The HACK
If the brake warning light came on, and you replace the pad AND the brake sensor, then the computer is going to assume the sensor is still cut all the way through and continue to keep the warning light lit at all times.

Hence you will need to take a trip down to the dealership service department and have them RESET your ECU's fault code for you.

Not necessarily. Twist the key to "ignition on" position (without starting the car) for 30sec and the amber circle will disappear.

http://www.bimmerfest.com/forums/showthread.php?s=&threadid=14147

mullhaupt
01-09-2003, 11:04 PM
Ive been working on bmws for 20 + years now and first I can tell you is that when you do a brake job on a bimmer you need to change rotors with pads. The brake pad material is actually stronger than the rotor itself., Unless you are using some cheap crap like autozone parts. The reason for this is that when your pads and rotors get heated up (and they do) the brake pedal will not get hard and your brakes will work, It wont cause brake fade Most mechanics have felt this especially if you ever adjusted drum brakes to tight, those drums get red hot and then the brakes just dont work and the pedal gets hard. Rotors and pads arnt that expensive, we get them from a auto parts distributer (worldpac) and a set of german pads and rotors is just over 80 dollars. I am not sure what list is. Dont buy cheap pads, when you go up the mountains and go through the twisties under heavy braking you will notice the pedal getting harder and the brakes not working as well like the booster isnt working. As for brake circuit sensors you have two one on the left front and one on the right rear, Ive only seen 4 sensors on a audi ,never on a bimmer. all it is is two wires connected together at a plastic connector which is shoved in the back of the pad, (approximately 11 volts with the engine off and key on) when the inside pad gets about a little more than a eighth of an inch it brakes this plastic connector and the wire seperates and the voltage isnt completed back to the control module and then the pad sensor light comes on When you put a new sensor in you will have to drive it a couple of hundred feet before the light resets itself

Pinecone
01-10-2003, 02:22 AM
Originally posted by mullhaupt
Ive been working on bmws for 20 + years now and first I can tell you is that when you do a brake job on a bimmer you need to change rotors with pads. The brake pad material is actually stronger than the rotor itself., Unless you are using some cheap crap like autozone parts. The reason for this is that when your pads and rotors get heated up (and they do) the brake pedal will not get hard and your brakes will work, It wont cause brake fade Most mechanics have felt this especially if you ever adjusted drum brakes to tight, those drums get red hot and then the brakes just dont work and the pedal gets hard. Rotors and pads arnt that expensive, we get them from a auto parts distributer (worldpac) and a set of german pads and rotors is just over 80 dollars. I am not sure what list is. Dont buy cheap pads, when you go up the mountains and go through the twisties under heavy braking you will notice the pedal getting harder and the brakes not working as well like the booster isnt working. As for brake circuit sensors you have two one on the left front and one on the right rear, Ive only seen 4 sensors on a audi ,never on a bimmer. all it is is two wires connected together at a plastic connector which is shoved in the back of the pad, (approximately 11 volts with the engine off and key on) when the inside pad gets about a little more than a eighth of an inch it brakes this plastic connector and the wire seperates and the voltage isnt completed back to the control module and then the pad sensor light comes on When you put a new sensor in you will have to drive it a couple of hundred feet before the light resets itself

You are right about the sensor. Every other brake sensor I have seen work the same way. Wear BREAKS the circuit and turns on the light. Of course, if someone forgets to put the sensor back in the slot in the pad, it won't work. If you cut the wire, the light turns on.

As to the rest, you have a few things backwards. When brakes fade they do so in a couple of ways. PAds fade is where you have normal rake pressure, but the car doesn't stop. The pedal doesn't get harder, but may feel that way because youa re pushing more trying to get some braking action. This can trash both the pads and rotors from overheating. What typcially happens is the pads get too hot and transfer pad material to the rotors leading to a shuddering feel to the brakes (commonly confused as rotor warp).

Fluid fade is where the brake fluid gets hot and boils. The pedal goes to the floor and no stopping. his is why you want to flush your system every couple of years.

As to changing rotors at the same time as pads, if the rotors are that worn, fine. But I measure the rotors and compare them to stock rotors. If I have wron more than 1/2 of the diffference between stock and minimum allowable thickness, I change them. If not, then I don't change them. You don't change you pads by mileage, so why would you change the rotors just because you change your pads?

As to knocking AutoZone pads, I wonder if you know that AutoZone sells Performance Friction pads These are one of hte top pads available. They carry both the PF97 and Z compounds.

mullhaupt
01-10-2003, 08:33 PM
Originally posted by Pinecone
You are right about the sensor. Every other brake sensor I have seen work the same way. Wear BREAKS the circuit and turns on the light. Of course, if someone forgets to put the sensor back in the slot in the pad, it won't work. If you cut the wire, the light turns on.

As to the rest, you have a few things backwards. When brakes fade they do so in a couple of ways. PAds fade is where you have normal rake pressure, but the car doesn't stop. The pedal doesn't get harder, but may feel that way because youa re pushing more trying to get some braking action. This can trash both the pads and rotors from overheating. What typcially happens is the pads get too hot and transfer pad material to the rotors leading to a shuddering feel to the brakes (commonly confused as rotor warp).

Fluid fade is where the brake fluid gets hot and boils. The pedal goes to the floor and no stopping. his is why you want to flush your system every couple of years.

As to changing rotors at the same time as pads, if the rotors are that worn, fine. But I measure the rotors and compare them to stock rotors. If I have wron more than 1/2 of the diffference between stock and minimum allowable thickness, I change them. If not, then I don't change them. You don't change you pads by mileage, so why would you change the rotors just because you change your pads?

As to knocking AutoZone pads, I wonder if you know that AutoZone sells Performance Friction pads These are one of hte top pads available. They carry both the PF97 and Z compounds.


You are right about what I said I just read it and I guess I was a little tired . But about the rotors of all the bimmers Ive seen the rotors are worn down so much that there is a lip on the edge of each side of the rotors of at least an eighth of an inch. This is due to using the harder pads such as ATE : Pagid We are not to familiar with how the Performance Friction Pads wear. I have heard they work well but have not seen them after 30 or 40 thousand miles to say what they do to rotors. Like most american and Japanese cars I know you can turn the rotors,and a rotor usually lasts two brake jobs. but for some reason doing this to BMW's the custumer usually will come back having brake shatter, this is why when they are pretty worn down we recommend Rotors, Now a days there are many manufacturers that do not recommend turning rotors.

Pinecone
01-11-2003, 10:27 AM
Originally posted by mullhaupt
You are right about what I said I just read it and I guess I was a little tired . But about the rotors of all the bimmers Ive seen the rotors are worn down so much that there is a lip on the edge of each side of the rotors of at least an eighth of an inch. This is due to using the harder pads such as ATE : Pagid We are not to familiar with how the Performance Friction Pads wear. I have heard they work well but have not seen them after 30 or 40 thousand miles to say what they do to rotors. Like most american and Japanese cars I know you can turn the rotors,and a rotor usually lasts two brake jobs. but for some reason doing this to BMW's the custumer usually will come back having brake shatter, this is why when they are pretty worn down we recommend Rotors, Now a days there are many manufacturers that do not recommend turning rotors.

It happens. :)

BTW one o fhte reasons why brake pads are harder theses days and hard on rotors is the change from any use of asbestos.

And the funny thing, due to the structure, asbestos containing brake pads did not release asbestos fibers. :)